Need help with analyzing this combination circuity

[shemer77]

Homework Statement

the circuit
http://img15.imageshack.us/my.php?image=38052495.gif
http://img15.imageshack.us/my.php?image=38052495.gif
the chart
http://img3.imageshack.us/my.php?image=chart.gif
http://img3.imageshack.us/my.php?image=chart.gif
I need to fill out the chart, I have shown what's given and what I think I have solved correctly. I need help with figuring out the rest!


2) determine the current through each resistor
http://img3.imageshack.us/my.php?image=current.gif
no idea on how to approach this

Homework Equations

The Attempt at a Solution

 

[mplayer]

For the first 2 images:
I would suggest simplifying the circuit into its Voltage source and a single R_eq. You can use this information to determine the source current. Then expand the circuit back out to its original form, and determine the voltage drops across each element or element combination. You will then have more than enough information to complete your table by just applying Ohm's Law where needed.

 

[mplayer]

2) determine the current through each resistor
http://img3.imageshack.us/my.php?image=current.gif
no idea on how to approach this

Have you learned mesh analysis?

 

[shemer77]

nope
for the first one how can i get req? I don't know any of the resisort values
and is the total resistance for 2, 4.5?

 

[mplayer]

Oh OK, I didn't see that at first. Forget R_eq.

Your R₁ is correct, but your R₂ isn't. I think you had the right idea but just messed up the math.

Think about the given currents in R₁ and R₂ and how that relates to the source current. With that, you can know what the currents are through all the elements, and that may help you to figure out many of the values. Also, remember that the total sum of the voltage drops/increases in the loop is equal to zero.

 

[mplayer]

nope
[...]
and is the total resistance for 2, 4.5?

No, total resistance for 2) isn't 4.5 ohms. I would suggest redrawing the circuit so it resembles the one in the first part. The connections will be much clearer.

 

[shemer77]

2) would it be 3 for total resistance?
1)

Your R1 is correct, but your R2 isn't. I think you had the right idea but just messed up the math.

what about my r1 is correct and what about my r2 isnt?

would 5=current for r3?

 

[mplayer]

1)
what about my r1 is correct and what about my r2 isnt?

would 5=current for r3?

You are given the current through both resistors, R₁ and R₂. You are also given the voltage across R₁. Notice that R₁ and R₂ are in parallel, which means that the voltage across R₁ is also the voltage across R₂, which you had correct. So you have the currents through both of the resistors (given) and the voltages across the two resistors (the same).

V=IR ; R = V/I

Your resistances for R₁ and R₂ should not be equal. You have them listed in your table as being equal.

EDIT: Yes, current through R₃ would be 5 A. Notice that this is the source current.

2) would it be 3 for total resistance?

No. Did you try redrawing the circuit so it resembles the circuit in 1)?

 

[shemer77]

got it, it should be r1=2 and r2=3, so is r5's current 4? and r6's current 5? and r3's v=15?
2) isn't i3 in series with the battery, and i1 and i2 are in series with each otehr and they are parallel with i3?

 

[mplayer]

got it, it should be r1=2 and r2=3, so is r5's current 4? and r6's current 5? and r3's v=15?

Yes to all, you are on the right track.

2) isn't i3 in series with the battery, and i1 and i2 are in series with each otehr and they are parallel with i3?

Yes, R₃ is in series with the battery. R₁ and R₂ are not in series with each other though, they are in parallel. R₃ is then in series with the combination R₁||R₂

 

[shemer77]

2) so req=10? if that's right, what would I do next?

1) r5's resistance=2, r4's voltage = 8,r4's resistance=8,? how would i figure out I and R for the battery and how would i figure out V and R for r6?

 

[mplayer]

2) so req=10? if that's right, what would I do next?

Yes. Solve for the source current, and then the currents in the parallel part.

1) r5's resistance=2, r4's voltage = 8,r4's resistance=8,?

Correct.

how would i figure out I and R for the battery

Assuming the source (battery) is an ideal source, it has no internal resistance. The current through the battery is the source current you figured out earlier.

and how would i figure out V and R for r6?

Think about it like this. You have the voltage developed by the source (battery). You also have the voltage drops across all the resistive elements in the loop except for one, V_R6. Apply KVL and you should be able to easily get the voltage drop across R₆.

 

[shemer77]

thanks man, I really owe you a lot, just one more question, I am going to make a new thread.

 

[mplayer]

No problem, glad to help.